DVD (Digital Versatile Disk)

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Introduction

DVD initially stood for Digital Video Disc but now stands for Digital Versatile Disc. Like a CD, DVD is an optical storage system for read-only, recordable and rewritable applications. But, being similar to a CD in many ways, DVD is considered to be a CD future replacement.

The main differences between the CD and DVD are summarized in the following table:

Feature	DVD	CD-ROM
Substrate diameter / thickness (mm)	120 / 1.2	120 / 1.2
Sides	1 or 2	1
Layers per side	1 or 2	1
Capacity (GB)	4.7, 8.54, 9.4, or 17	~ 0.7
Track pitch (microns)	0.74	1.6
Min pit length (microns)	0.4 - 0.44	0.83
Linear velocity used for scan (m/s)	3.5 - 3.84	1.3
Laser wavelength (nm)	635 or 650	780
Numerical aperture	0.6	0.45
Modulation	8 to 16	EFM (8 to 17)
Error correction code (ECC)	RSPC	CIRC
Durability and dust/scratch	same as that of CD	high

The main features of the DVD formats can be summarized as follows:

Backwards compatibility with current CD media (at least the newest models of DVD drives)
Physical dimensions identical to compact disc with total thickness equal to 1.2 mm, but with capacity at least 7 times larger than that of CD.
Capacities of 4.7 GB, 8.54 GB, 9.4 GB, and 17.08 GB, depending on the disk structure.
Single-layer/dual-layer and single/double sided options.
DVD replication process is similar to that used for compact disks.
A disc-based format means fast random access like in hard drives and CDs and unlike tapes.
Designed from the outset for video, audio and multimedia. Meets the requirement for 133 minutes of high quality video on one side of a disk.
DVD-ROM for enhanced multimedia and games applications.
DVD-Video for full length high quality movies on one disc.
DVD-Audio for higher quality music, surround sound and optional video, graphics and other features.
All formats use a common file system.
Copy protection built into standard (unless it is broken...)

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